Pickup trucks are motor vehicles with a front passenger area, often referred to as a cab, and an open top rear cargo area, often referred to as a box. The box usually has a substantially flat bed from which two sidewalls and a forward interconnecting headboard extend upwardly therefrom. Pickup trucks may also employ a bottom hinged door, commonly referred to as a tailgate, hinged at the rear edge of the bed and closable to provide a fourth wall for the cargo area. Cabs and boxes may be separate assemblies or part of the same unibody structure. Pickup trucks are popular largely because the box allows them to be utilized in so many different ways, including carrying a variety of types of cargo and towing various types of trailers.
Traditionally the majority of body structures on pickup trucks have been formed from steel alloys. Through years of experience, pickup truck designers have learned how to engineer steel truck body parts that withstand the variety of demanding pickup truck applications. The current regulatory and economic environments have increased the importance of making pickup trucks more fuel efficient as well as functional and durable. One way to reduce the fuel consumption of a vehicle is to reduce vehicle structure weight.
Aluminum alloys typically have a higher strength to weight ratio than steel alloys. Consequently, replacing steel with aluminum offers the potential for weight reduction; however, the elastic modulus of aluminum is generally lower than the elastic modulus of steel. In addition, fabrication techniques and methods of joining parts that work well for steel parts may not work well for the same aluminum part. Because of these and other differences, simple material substitution does not necessarily produce an acceptable design.
Aluminum alloys are generally identified by a four-digit number, the first digit of which typically identifies the major alloying element. When describing a series of aluminum alloys based on the major alloying element, the first number may be followed by three x's (upper or lower case) or three 0's (zeros). For example, the major alloying elements in 6xxx or 6000 series aluminum alloy are magnesium and silicon, while the major alloying elements of 5xxx or 5000 and 7xxx or 7000 series is magnesium and zinc, respectively. Additional numbers represented by the letter ‘x’ or number ‘0’ in the series designation define the exact aluminum alloy. For example, a 6061 aluminum alloy has a composition of 0.4-0.8% Silicon, 0-0.7% Iron, 0.15-0.4% Copper, 0-0.15% Manganese, 0.8-1.2% Magnesium, 0.04-0.35% Chromium, 0-0.25% Zinc, and 0-0.15% Titanium. Different alloys provide different trade-offs of strength, hardness, workability, and other properties.
There are also five basic temper designations that may be used for aluminum alloys, which are: F, as fabricated; O, annealed; H, strain hardened; T, thermally treated; and W, as quenched. The temper designation may be followed by a single or double digit number for further delineation. For example, aluminum with a T6 temper designation has been solution heat treated and artificially aged, but not cold worked after the solution heat treatment, or such that cold working would not be recognizable in the material properties.
As noted above, one of the benefits of using aluminum alloys is their high strength to weight ratio; however, such alloys tend to be more expensive than traditional steel alloys. Therefore, to the extent that higher cost alloys are used in a vehicle, such as a truck, it would be desirable to have a modular construction to allow replacement of components on a more individualized basis. One portion of a vehicle that could benefit from such a construction is in regard to the pillars which extend between a roof rail and a lower support such as a rocker. Conventional pillars may wrap around one or both of the roof rail or rocker, and may be, for example, welded in place. In case of damage to a pillar, conventional designs may require replacement of the rocker supports and even the entire roof rail structure. Therefore, a need exists for a modular vehicle body structure that facilitates replacement of such pillars without the need to replace all of the other structures to which they are attached.